In an example, a method includes obtaining object model data describing at least a portion of an object to be generated by additive manufacturing. A color value of a first portion of the object to be generated may be determined, wherein the color value is based on a first color and a second color, different from the first color. Object generation data to generate the object using a fusing agent of the first color and a build material having the second color may be determined by defining a first region of a layer of build material to which fusing agent is to be applied defining a second region of the build material to which detailing agent is to be applied to define an edge of the object and defining a spacing region of build material to separate the first region and second region, wherein the spacing region is defined using parameters selected to provide the color value.